Fuse



ff 3" E l E wie v 1927' EENNEW USE Filed Sept. 25, 1926 1' N VEN TOR.

Bey/7m m AA TToRNEYs Parenteel June 7, 1927.

UNITED STATES PATENT OFFICE.-

CHARLES BENNETT; 0F DECA'LLUR, GEORGIA.

FUSE.

Application lei September use for this purpose in circuits of 2500 volts to 132,000 volts or over with which particularly the present invention deals. Certain features of the invention are applicable to other structures vand devices than fuses, strictly so called, and 'these broader applications ot the invention are to be understood to fall Within the scope oil the sub-joined claims.,

ln the accompanying drawings- Fig. l is a broken section'through a fuse embodying rny invention in a construction suitable for voltages up to about 44,000 volts; and

Fig. 2 is a similar vievv through a iuse appropriete for higher voltages.

The constructions shown merely il lustrative ori my invention and may be vari`s e e l ouslymodiiied, While still embodying the characteristics of operation and construction which l claim as my invention.

Referring to Fig. l dealing with con 'struction appropriate ior voltages up to ille 000, l have shown the 'lense strip or vvire l5 attached at its opposite ends to similar conu tact ierrules i6 and l?. Each ierrule is spool-sha'pecll1 the end anges i8 lll there` ot spanning a spring terminal contact (notv shown) `which gri s the barrel or body ci ieerrule.. l'nterrne iate the end flanges lo@ ai I 'i9 the ierrule is provided with an interior transverse web 20 centrally aperturcrl at 2l to permit the passage oi the iiuse end therethrough. The projecting iuse end is orlset against the outer tace olf 'the web 2Q, against which it is clamped by a screw 23 through an interposed metallic Washer 24. Prelerabl a tight fitting washer 25 'ci rubber, or otier displaceable material., is interposed between the plug 23 and Washer 24 to seal the joint against the escape ci gases which form on the blowing of the fuse.

Encasing the fuse strip throu hout its lengthbetwen the ferrules 16 an 17, is a renewable casing comprising a strong Walled tube 26 of non-shattering but rupturable, insulating material which is non-inflam- 23, 71926. Serial '.io. 137,309.

mable under operating conditions and of such character that dangerous carbonization of thewall does not occur on the blowing of the' fuse. l have found poor grade rubber a most satisfactory material since its fillers render 1t in effect non-inammable under Voperating conditions Without losing the desired yielding and flexible characteristics of the casing.

Each end of the casing 26 is provided with a head ange 27 against which bears a screw plug 28, by means of which the tube endis firmly clamped against the diaphragm 20 with the small bore of the casing in register with the fuse aperture 2l in the diaphragm.

The pressure of the metallic gases gener`= ated Within the casing by the burning ci the fuse is very high due to the restricted cross-1 section of 'the casing bore. The end sealsy and the Walls ci the renewable casing are r accordingly strong: for example7 suticiently strong to withstand an internal pressure or? about 100 pounds per square inch., When the fuse blows, the pressure Within 'the casing exceeds this and the casing ruptures at its Weakest point, The escaping may cause damage unless pro erly acte-d and may even cause the establlshment of an arc between the -fuse terminals and 'erior to the casing. l prefer therefore to itely locate Weak spot in 'the 'tubs vval. This may be accomplished in retirions For ea'anuole in' Fig.. 'l l have indio a minute puncture 29 extending thro f wall of the casing at point appro: ately niiclvvayci. its length. l spring band clip 30 normally closes the puncture, but is pro jected from the casing by the escaping gas.

lne rupture oi the casing therefore occurs this weakened point7 and the hot escapes direction of the puncture. may thus be deiinitely controlled. rupture occurs, the fertiles? terminals and adjacent equipment remain uninjurerl by arc or gas. llo arc between' the terminals beconies established and while the cas stroyed, it is inexpensive and is reaely and simply replaced. 'Under no circumstances can a dangerous explosion occur is 'frcquently the case with oil circuit breakers.

The construction shown in lig. 2 is adapted to heavy voltage duty. A :fuse carrying current oi lll OOO volts and over is subject to disintegratlon as the result of corona ac tion. To protect the ruse against this phelli) `annular space therebetween with some'high resistance ilu-id 33 (such e. g. as distilled water) which is non-injurious to the mate- 1 rial of the casings, and carries enough curlthe outer casing, it serves in an rent to serve as a corona shield: It may also. be of such character as to aid 1n extinguishving the fiame or arc on rupture of the -fuse casing.

' The ferrule construction is adapted to such an arrangement. 'Thus, the flange 34 at the tube end of the ferrule barrel 35 is extended to forma housing for the head 3 6 of the outer tube 32, the metal washer 37 and screw plug 38. The metal washer 37 lies against the end of the ferrule body, and its central boss 39'surrounds the inner tube 31 and enters the end of the tube 32, thus centering the tubes'with res ect to each other. This washer also establis es electrical connection between the fiuid corona shield 33 and/the ferrule. The screw plug 38 bears against the .head 36 of the outer tube and clamps it against the washer 37 and ferrule in a firm liquid sealed `joint.

Y The head of the inner tube 31 is pressed against the outer face `of the washer 37 by the screw plug 40, which also clamps the offset fuse end between the washers 41 and 42 which are in contact with the ferrule.

While the wall of the tube 31 may be weakened at some point as at X, to determine a rupture point, obviously no uncture can be ermitted which would a mit the surroun ing liquid to the interior of the tube. As a matter of fact a rupture point is of relatively little importance since the flame from the fuse tube at once converts the liquid 33 into vapor, and while this vapor may have suicient pressure to rupture event `to suppress the fiame and render t e rupture innocuous. i

I have mentioned above the fact that the tubes 26, 31, and preferably also the corona casing 32, are of, non-inflammable material, and I have mentioned low grade rubber as suitable for such use. Rubber of this character, however, deteriorates when subjected to the actionof the elements. I therefore propose to protect the casings by a ver' thin skin 43 of s nthetic rubberwhich wi l withstand sunlig t, etc., and screen the low grade body material of the tube from actinic rays and other deteriorating in'uences.

When excessive current is imposed on the fuse, the fuse wire or strip 1s consumed throughout the major portion of its len h. A very heavy gas pressure builds up wit in the casing and ruptures the latter. On the relatively low voltage fuses, excessive pressure ruptures the casing at its weakened point 29, and the hot gases escape at this point. There is no arc formation, however, between the contacts with which ,theV ferrides 16 and' 17 are engaged, and the circuit is promptly broken. It is an easy matter to replace the rubber casing and the fuse by unscrewing the plugs on opposite sides of the ferrule diaphragm. On the high voltage fuses in which the fuse casin is surrounded by the corona shield liquid, t e latter helps to chill the hot gases that escape the fuse casing' on rupture of the latter and creates a condition which' aidsin extinguishing any are which might tend to form.

The exact explanationof what occurs on the blowing of the fuse cannot now be given by Ireason of the rapidity of action and the consequent difficulties of observation. It is my presentybelief however, that the sudden escape of the gases from the casin not only creates, by Jet action, a partia vacuum within the casing (and a vacuum is inimical to arc maintenance) but also exhausts practically all of the fuse metal. in gaseouscondition, with the result that on condensation of the slight amountl of metallic gas that remains in thecasing the metallic deposit on the inner wallthereof is so slight and the metallic particles so separated that no current path isestablished thereby between the opposite end ferrules. The charring of the inner wall of thecasing by the flame is slight by reason of the character of the material of the` Casing which, in large part, is noncarbonizing under ythe conditions of fuse rupture.

lt is possible that other insulating matcrial could be used for the casing, if of sufficient strength to withstand the heavy pres sures generated incident to the blowing of the fuse and otherwise suitable, but I prefer low grade, substantially non-inflammable rubber composition, by reason of its economy, its non-shattering character on rupture, its flexibility and resilience, and the facility with which it may be jointed to the ferrules to form tight seals.

Of course the size of the fuse wire will vary with the current that it must carry, and the strength of the casing walls must vary in accordance wih the internal pressures likely to be encountered. The length of the fuses and of their casings will vary with the voltage. For example, for a 2500 volt fuse an over-all length of 12 inches will suffice, while for a 132,000 volt fuse an overall length of approximately 4 feet is desirable. It will e realized that the initial expense of fuses of this character is negligible as compared with' the equipment now in general use for like service. Yet I have found that fuses of the construction stated function reliably without danger to surrounding equipment or fuse terminals.

I have shown the fuse casing as a renewable element, along with the fuse strip, be-

lll)

tween the end ferrules. It may be preferfuse chamber of restricted dimensions, said connection therewith, a sealed fuse casing' of non-inflammable flexible insulating macasing being formed of non-inflammable yieldable, flexible insulating material susceptible to -rupture at a point between said ends under high internal pressure.

v2. In a high voltage fuse, a fuse casing sealed at itsopposite ends against rupture thereat on the `blowing of the fuse having a bore of restricted cross-section to aord a fuse chamberof restricted dimensions, said casing beingformed of non-inflammable yieldable, flexible insulating material susceptible to rupture at a point between said ,ends under hi h internal pressure, said casing being wea cned at a point intermediate` its endsto locate a definite rupture point.

3. A high voltage fuse comprising a pair of endcontact ferrules, a'. fuse element extendingtherebetween, and a fuse casing of non-inflammableviexibl'e insulating mate-A rial susceptible' to rupture under heavy internal stresses, said casing having Va fuse' chamber of 'restricted cross-sectional area and being sealed at said Iferrules against gas escape lat rupturing pressure.

4. In a high voltage fuse, a: pair of metallic end ferrules, a fuse velement in electrical terial upturing on heavy internal pressure, and secured to the ferrules to revent gas escape at the opposite ends oi` t e structure in the direction'o the casing bore-on rupture of the casin 5.' In a high voltage fuse, a palr of metallic end ferrules, a fuse element in electrical connection therewith, and a'tubular fuse casing of non-iniiammable flexible rubber composition capable O withstanding heavy internal fpressure and secured to the ferrules to prevent gas escapel at the opposite ends of the structure.

6. lIn a high voltage fuse,- a pair of metallic end e'rrules, a fuse element vin electrical connection therewith, and a flexible tubular fuse lcasingof non-inflammable rubber composition capable of withstanding heavy internal pressure and secured to the ferrules to-prevent gas escape at the opposite ends ofthe structure, said iiexible casi g having' a protective skinv adapted to preve t deterioration of the casing on exposure to the elements.

7. As an element'of a fuse structure, an endseaied tubular fuse casing of non-inflammable flexible insulating material capable o'f withstanding high lnternal stresses.

8. As an element of a fuse structure, a sealed tubular .fuse casing of yieldable, non- `infiammable insulating material capable of withstanding high internal stresses, but weakened at a predetermined rupture point between its ends.

9. A fuse comprising a fuse element, an insulating casing therefor, and a liquid corona shield surrounding 'said casing.

10. A fuse structurecomprising a pair of concentric insulating casings, a fuse element within the inner casing, and a liquid'corona shield in the annular space between the casings.

11. A=fuse -structurecomprising a pair of fuse terminals, a fuse extending therebetween, and a corona shield in electrical contact with said terminals.

In testimony whereofvI have signed my name to this specification.

CHARLES E. BENNETT 

